The present invention relates to a circuit which causes and controls the running of a synchronous motor provided with a polyphase armature winding.
Circuits of the type under discussion have been known. One of such circuits has been disclosed in DE-OS 30 42 819. The circuit disclosed in this reference is realized so as to successively lock individual phases of the polyphase armature winding by current valves each of which is connected in series with the respective phase of the armature winding positioned in the stator of the motor, and which is arranged between the end of the respective winding phase and the zero potential. The other or opposite ends of the phases of the armature winding are joined together at a star point and are connected via the network switch to the positive potential of the d-c voltage network.
A switch signal generator and the logical stage for a logical control of the current valves are realized by voltage comparators, logical combination members and a ring counter the parallel outputs of which are connected to the control input of the current valves. Voltages which are induced in the winding phases, which are connected one with another in a cyclical manner due to the locked current valve, are compared with each other in the voltage comparators; this results in the output signal in the respective comparator when the voltage induced in the following winding phase is greater than the voltage induced in the previous winding phase. These output signals of the voltage comparators are logically combined ("And") with the output signals of the ring counter in such a fashion that the switch signal can be then applied to a monoflop only when current passes through that following wnding phase with the higher induced voltage due to the opening of the respective current valve. The output of the ring counter connected to the control input of this current valve is connected to the high-potential. The ring counter further counts pulses with the positive flanks of the output pulses of the monoflop so that by this time the high-potential lies at the next counter output, and the current valve, which has been opened for a moment, is closed, and the next-positioned current valve in the cycle becomes opened.
Inasmuch as in the inoperative position of the rotor or the runner of the synchronous motor, no information is available by such an adjustment an auxiliary tact generator is provided, which starts the ring counter to start the motor, and these steps are very slow since they take, for example 0.5 sec. to start the motor. As soon as the direction of rotation of the rotor, the condition of the counter and the voltage points of the induced alternating voltages are combined the synchronous motor becomes self-controlled and accelerates with a maximal torque until its speed reaches the operational value.